Been ♥♥♥♥ed

Here is a mods standard reply to people who have been h@cked.
There really is nothing we can do on the community forums to help you, so please contact Support using the in-game reporting or e-mail them directly at: clashofclans.feedback@supercell.net

I know there are not a lot of options once another device has your game on it. Below is my standard reply to h@ck posts, good info for future reference. Good luck with support.

Substitute Google+ for Gamecenter and Google for Apple if it's Android (I'm using an old post)
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I know of NO-NONE-ZERO cases of anyone actually h@cking Apple's Gamecenter to get to a Clash of Clans village.

A few facts/misconceptions:

Supercell only supports one account per device. Apple considers an iOS device to be a single user device. If a village is authorized to it (either by starting a game, or loading it via gamecenter) it is permanently authorized to that device. The Gamecenter password is only needed the very first time you load the game. Once a device "Owns" the game, changing the Gamecenter password, logging out of gamecenter, even deleting the app doesn't remove your game from that device. If you sell or trade your iOS device, doing a factory reset is the only way to ensure the next user can not play your game. If you authorize your game to someone else's device, even a factory reset may not remove it, as they can do an iCloud or iTunes backup/restore of their device to include your village.

Gamecenter in relation to Clash of Clans is designed to attach YOUR village from YOUR device to allow you to move YOUR village to a new device YOU own. It is not an authentication method to log into and out of different devices, it's a transfer mechanism. You should never load your village onto a device you do not control. Once a village is loaded onto a device, it is permanently authorized and playable from there. Neither Apple, nor Supercell can remove a village from a device which was properly loaded at one point. It is not legally or technically possible. Once a device is authorized, the device can not be blocked or restricted.

Morale of the story is NEVER load your village on a device not owned/controlled by you, allow someone else to log onto your device with a different Gamecenter, or give out your Gamecenter account info to anyone.

So, knowing the above, 100% of the time folks claim to be h@cked, or someone is playing their game, it boils down to:

A) a family member plays on the iOS device without you knowing it
B) you gave your gamecenter password to a friend who used it to load your game
C) you gave your gamecenter password to one of those 3rd party gem sites
D) you logged onto a friends iOS device to play at one point, thinking logging out of gamecenter or deleting the app will prevent them from playing it (it doesn't)
E) you sold/traded/gave away an iOS device you had once played the game on without doing a factory reset and they still have access to your CoC village.
F) a friend logged in with a clean gamecenter answered the prompts and transferred your village to their GC, and loaded it on their device later (if your village wasn't attached to your own gamecenter)
G) Someone sent you a "Free" account - while logging into this new gamecenter you actually transfer you village to this empty gamecenter account and they can then load it on their device. (If your village wasn't attached to your own gamecenter)

If it's your little brother playing, it's easy to solve, if it's an ex-best friend who can now play your game, there are not a lot of options.